Project Summary/Abstract: An abnormal accumulation of potentially pathogenic commensal populations, namely pathobionts, is thought to contribute to the pathogenesis of inflammatory bowel disease (IBD). However, what bacteria can be classified as disease-associated pathobionts and how these pathobionts promote intestinal inflammation in IBD remains poorly understood. The long-term goal of this proposal is to develop new therapeutic strategies that selectively target IBD-associated pathobionts and their downstream inflammatory pathways without influencing beneficial commensal bacteria. Our preliminary data and recent studies have demonstrated that oral bacteria are enriched in the intestinal mucosa of IBD patients and might contribute to the inflammatory processes occurring in the gut in IBD. The objective of this application is to determine the mechanisms by which ectopic colonization of oral pathobionts elicits gut inflammation in IBD. Our preliminary data demonstrate that oral inflammation induces the expansion of pathobionts in the oral cavity. An accumulation of pathobionts in the oral cavity results in increased levels of colonization in the gut. Gnotobiotic IBD-prone IL-10-deficient mice that are colonized by oral pathobionts develop severe colitis, while mice colonized by healthy oral microbiotas do not. Moreover, our preliminary data also demonstrate that oral pathobionts induce DNA damage in colonic epithelial cells and lamina propria macrophages. Based on these preliminary results, our central hypothesis is that pathobionts, originally found in the dysbiotic oral mucosa, contribute to the pathogenesis of IBD through their ectopic gut colonization and their genotoxic activity. This hypothesis will be tested by pursuing the following three specific aims: In Aim 1, we will examine the impact of the colonization of oral pathobionts on colonic epithelial integrity. We will determine the localization of oral pathobionts in the gut and their effect on epithelial barrier functions in vitro and in vivo. In Aim 2, we will define the impact of oral pathobionts on inflammasome activation in intestinal macrophages. We will identify the inflammasome proteins that are involved in oral pathobiont-driven inflammation in vitro and in vivo. In Aim 3, we will determine the extent to which the genotoxic activity of oral pathobionts contributes to their colitogenic capacity. The rationale for the proposed research is that the identification of pathways by which oral pathobionts elicit intestinal inflammation will result in new and innovative ways to treat IBD. Furthermore, inhibition of the growth of pathobionts in the oral cavity (e.g., by treating oral inflammation) should also reduce the risk of flares/IBD exacerbation by limiting the supply of colitogenic bacteria.